1. Field
Embodiments of the present disclosure relate generally to landing gear and, more particularly, to a semi-levered landing gear and an associated method of positioning the bogie beam of the landing gear using a telescopic hydraulic actuator.
2. Background
Many airplanes include landing gear to facilitate takeoff, landing and taxi. The landing gear of some aircraft includes a shock absorber that is pivotally attached to a bogie beam at a distal or lower end thereof. The shock absorber may also be referred to as a shock strut. The bogie beam includes two or more axles upon which tires are mounted. In this regard, the bogie beam may include a forward axle positioned forward of the shock absorber and an aft axle positioned aft of the shock absorber. Upon takeoff, an airplane having a conventional landing gear with forward and aft axles will pivot about the pin that attaches the bogie beam to the shock absorber such that all of the landing gear tires have an equal load distribution.
In order to provide additional ground clearance for rotation of the aircraft during takeoff, semi-levered landing gear mechanisms have been developed. A semi-levered landing gear fixedly positions the shock absorber and the forward end of the bogie beam during takeoff such that the forward axle is in a raised position relative to the aft axle when the airplane has left the ground. As such, the aircraft pivots about the aft axle, rather than the pin that pivotally connects the bogie beam to the shock absorber, provided that the extend pressure of the shock absorber has been increased sufficiently. By rotating about the aft axle, the landing gear height is effectively increased so as to provide additional ground clearance for rotation of the aircraft during takeoff. As a result, the takeoff field length (TOFL) of the aircraft may be reduced, the thrust used by the engines may be reduced, or the weight carried by the aircraft may be increased while maintaining the same takeoff field length.
In order to provide for rotation of the aircraft about the aft axle during takeoff, a semi-levered landing gear locks the bogie beam in a “toes-up” attitude such that the tires mounted upon the aft axle support the aircraft, while the tires mounted upon the forward axle are raised above the surface of the runway. Following takeoff, the landing gear is generally stowed in a location such as a wheel well. In order to fit within a conventional wheel well, the landing gear is typically unlocked and the bogie beam repositioned in a “stowed” attitude prior to retracting the landing gear into the wheel well. Thereafter, during landing, the landing gear is lowered and the bogie beam is repositioned such that the forward axle is higher than the aft axle. Upon touch down, all of the wheels, including both those on the forward axle and the aft axle, equally bear the weight of the aircraft. Typically, the locking and unlocking of a semi-levered gear system, and the resulting repositioning of the bogie beam relative to the shock absorber, occurs without input from the pilot or the flight control system.
One type of semi-levered landing gear utilizes a mechanical linkage to lock the bogie beam during takeoff, but uses a separate mechanical linkage, termed a shrink-link, to reposition the shock absorber for retraction into the wheel well. The use of a shrink-link increases the complexity, expense and weight of the resulting semi-levered landing gear more than desired. Mechanical linkages also may not provide sufficiently desired damping during landing or bogie beam pitch dampening while on the ground.
Another type of semi-levered landing gear includes a locking hydraulic strut to lock the bogie beam in the desired orientation for takeoff. The locking hydraulic strut is essentially a locking actuator, but has a number of additional chambers and an internal floating piston. While a semi-levered landing gear having a locking hydraulic strut is suitable for some aircraft, the landing gear of other aircraft may not have sufficient clearance or room for the hydraulic strut to be positioned between the shock absorber and the bogie beam in an efficient manner.
Accordingly, it would be desirable to provide an improved semi-levered landing gear hydraulic actuator that may be used on landing gears that do not have sufficient space for housing a conventional locking hydraulic strut configuration. In particular, it would be desirable to provide a semi-levered landing gear that is both weight and cost efficient and that is not overly complex, while still satisfying the various operational requirements of the semi-levered landing gear.